読み書きの確認の前にファイルの存在を確認するように

source/src/main/java/one/nem/lacerta/source/file/impl/FileManagerImpl.java

@@ -88,14 +88,22 @@ public class FileManagerImpl implements FileManager {
 
     @Override
     public boolean isReadable() {
+        if (this.isExist()) {
             File file = this.path.toFile();
             return file.canRead();
+        } else {
+            return false;
+        }
     }
 
     @Override
     public boolean isWritable() {
+        if (this.isExist()) {
             File file = this.path.toFile();
             return file.canWrite();
+        } else {
+            return false;
+        }
     }
 
     @Override